Typical implanatable cardiac pacemakers include a self-contained power source. The time between implant and explant of such pacemakers is most commonly determined by the power-source life and, to maximize the like of the implanted pacemaker, a great portion of the overall pacemaker volume has been devoted to the power source.
Obviously, pacemaker life can be increased by increasing the size of the power source. However, in most instances this would require an increase in the size of the pacemaker which is contrary to the general pacemaker design criterion that the pacemaker be as small as possible. Thus, typical prior art implantable cardiac pacemakers have sacrificed pacemaker life in favor of pacemaker size in an optimization of those factors.
There has been an ongoing effort to increase pacemaker life and/or to reduce the pacemaker size through the improvement of power-source power density (the ratio of available power and volume) as well as the power-source life itself. Recent developments have seen improvement of the power-source systems commonly used to power cardiac pacemakers, such as a zinc-mercury system, for example, as well as the development of new power-source systems, one example of which is a lithium-iodide system. These differing power-source systems, while offering the advantage of increased pacemaker life and the possibility of a decrease in pacemaker size, have differing physical characteristics which heretofore has required independent design of the pacemaker unit to optimally incorporate the power source within the pacemaker package. That is, the power-source systems presently and soon to be available for use within a pacemaker come in a variety of sizes and shapes having circular, rectangular and square cross sections, for example. Additionally, some of the power-source systems must be hermetically sealed to isolate them from the remainder of the pacemaker unit while others need not be isolated in any manner.
There is no efficient system known to the prior art whereby the many sizes and shapes pacemaker power sources may be accommodated within a single pacemaker design, particularly in those instances where the power source must be isolated from the remainder of the pacemaker unit.